In lateral profile dorsal face of propodeum sloping obliquely from postscutellum, such that most of propodeum is posterior to scutellum (in contrast to normal queens, in which dorsal face of propodeum drops steeply from postscutellum and much of propodeum appears ventral to scutellum and postscutellum, Fig. 1); entire body, including scape, mandible, face, mesosoma, petiole, postpetiole, and fourth abdominal tergite extremely smooth and shiny, glass-like; propodeal spines completely absent; petiole and postpetiole robust, generally similar to worker in shape but completely lacking anteroventral petiolar tooth of any kind; remarkably devoid of erect setae or pubescence, funiculus and terminal segments of tarsi with typical subdecumbent pubescence, but no trace of pubescence or erect setae anywhere else on body; size characters as in Figures 4 and 5.

Biology

I have only three records of C. distansHNS from Costa Rica, two older museum collections from the Central Valley, and one collection from La Selva Biological Station in the Atlantic lowlands. It is clear from material elsewhere in the range of the species that distansHNS prefers seasonally dry, open or brushy habitats.

In general, distansHNS has very large colonies that are low density. The one La Selva collection I observed was from a recent treefall. A large dead trunk had fallen, bringing a large Bauhinia vine tangle down with it. Crematogaster distansHNS dominated the treefall, with columns of abundant workers spread throughout and streaming back to the canopy along lianas. I did not find any nest center or brood, but I did find two alate queens along with a worker aggregation in a hollow stick. In the Santa Marta region of Colombia I observed a distansHNS nest in a dead stick, and on another occasion I found workers tending Coccoidea on Cnidoscolus (Euphorbiaceae). In a second growth forest in Venezuela I observed columns of workers descending a tree trunk and spreading out onto an Inga sapling, where large numbers of workers were tending scale insects.

Nothing is known of colony founding, but queens exhibit a morphology often associated with social parasitism (see Natural History Overview). Kusnezov (1949) described descoleiHNS from a single alate queen and suggested that it was a workerless social parasite because of the small size and shiny integument. Kempf (1968) refuted this by reporting worker-associated colonies. The discovery of a colony of distansHNS at La Selva with queens identical to descoleiHNS confirms the synonymy of descoleiHNS under distansHNS. It is possible that Crematogaster distansHNS is a temporary social parasite, requiring colonies of host species to establish new colonies of its own, but it is not workerless.

Comments

This species can at first be confused with crinosaHNS and relatives because of the bare face, general lack of erect setae, and short upturned propodeal spines. The strongly bilobed postpetiole and the robust petiole with subrectangular dorsal face set it apart. There is a subtle mesosomal shape difference that is difficult to define, but involves a relatively compact and elevated promesonotum. These mesosomal and petiolar shape characters, along with the small shiny queens, are more like acutaHNS and relatives than crinosaHNS. Other than the superficial similarity to crinosaHNS relatives, there are no other Costa Rican species with which it can be confused.

The distansHNS complex occurs from southern Texas in the United States south to Argentina. Members of the complex share a characteristic mesosoma, petiole, and postpetiole shape, but they vary in details of surface sculpture and pilosity. The queens are small and with highly polished and smooth integument, but varying in details of pilosity and petiole shape. Kempf (1968) made a start in understanding this group, and a few additional notes are added here, but more material, especially queens associated with workers, is needed to make further progress. In the following paragraphs I outline geographic variation as I currently understand it, based on the few collections I have been able to examine and the published work of Kempf.

A single specimen from Hidalgo Co., Texas, USA, has a punctate face, a pair of setae on face, and no erect setae on mesosoma. A series from San Luis Potosí, Mexico, has a punctate face, a pair of setae on face, a pair on mesonotum, and a seta on each propodeal spine. The two worker syntypes of corvina MayrHNS 1870, from "Mexico," have punctate faces. One worker has a row of four setae on the pronotum, five on the mesonotum, two on the base of one propodeal spine, and one on base of the other. The other worker has one on the pronotum, seven on the mesonotum, three on one side and one on the other side of the dorsal face of the propodeum. These punctate forms at the northern limit of the range I identify as corvinaHNS, but it is clear there is considerable variation in pilosity, and they may grade into forms further south. Punctate faces reappear on two forms from South America: scelerata SantschiHNS from Argentina and scelerata taperensis BorgmeierHNS from Brazil, Pernambuco State. These are nearly identical to corvinaHNS but with a more developed anteroventral petiolar tooth. Thus punctate faces seem to occur at the margins of the range of the lineage. Like other amphitropical distributions, it is unknown whether this pattern is due to shared ancestry and some form of centripetal speciation, in which new forms replace older forms in the center of the range, or convergence due to similar selection pressures in marginal habitats.

Two series from Morelos, Mexico have most of face smooth but with distinct patches of punctation posteroventral to eyes and between eyes and antennal insertions. Thus they are intermediate in this character between corvinaHNS and other distans-likeHNS forms to the south. They have a pair of setae on the face, 2-4 setae on mesonotum, and a seta on each propodeal spine. The types of parvicepsHNS, from Sao Paulo state, Brazil, have similar facial sculpture, a combination of smooth and punctate. All remaining forms have the face completely shiny.

The series from Costa Rica and two series from Panama have one pair of setae on the mesonotum and none on the face, pronotum, or propodeum. The dorsal face of the petiole is relatively elongate, proportionally longer than the material from further north. The Costa Rican series from La Selva Biological Station has associated alate queens. These queens are identical in every respect to descolei KusnezovHNS. Crematogaster descoleiHNS was described from a single alate queen from Argentina. The queens are strikingly elegant, like glass figures, with no trace of setae or pubescence on most of body. The dorsal face of the petiole is proportionately quite long.

Material from Colombia and Venezuela, from which I have examined about ten worker collections from a variety of localities, shows a great deal of variation. Some collections from Venezuela appear identical to Costa Rican and Panamanian material. Others from the Santa Marta area of Colombia are also very similar, but have relatively shorter petioles. Finally, some collections from the Santa Marta area and departments of Antioquia, Huila, and Santander are very pilose, with multiple pairs of setae on both the pronotum and mesonotum, and multiple setae on the dorsal face and spine of the propodeum. Two of these collections have queens associated with them. The queens are quite similar in shape to the Costa Rican and descoleiHNS queens, but have abundant erect setae on the face and dorsal surfaces, and the petiole is shorter.

Kempf (1968) described his broad view of distansHNS based on many collections, mostly from southern South America. He described worker characteristics and variation that match the less pilose forms from Venezuela, Colombia, Panama, and Costa Rica. In his figure of the dorsal face of a worker petiole, it appears relatively short, like the short-petiole material from Colombia, rather than the long-petiole material from Venezuela and Costa Rica. He described the queen of distansHNS, based on collections from Rio de Janeiro and Sao Paulo states. He described the queen as being nearly identical to descoleiHNS, with the same general shape and degree of hairlessness, but with a relatively shorter petiole. He stated that descoleiHNS was a probable synonym of distansHNS.

It is possible there are multiple sympatric forms in the Neotropics, with queens being much more differentiable than workers. Putting the above observations together suggests the possibility there are at least three forms: (1) descolei-likeHNS, the queens of which are hairless and long petiolate, (2) a widespread form with hairless queens and short petioles, and (3) a setose form, with abundant setae on queens and workers. But much more queen-associated material and some thorough morphometrics will be needed to confirm or modify these patterns. I have followed the "synonym until proven distinct" approach by formally synonymizing descoleiHNS under distansHNS. But future work on the complex will require a reevaluation of all the synonymized forms.